The SPF (Sun Protection Factor) is conventionally used as a measure for indicating the ultraviolet protection effect of cosmetic products that provide protection against sunburn from ultraviolet radiation (e.g., so-called sun care products). The SPF is obtained using an in vivo SFP determination method such as the world-recognized International SPF Test Method (CTFASA/COLIPA/JCIA/CTFA: May 2006) that involves evaluating erythema reactions of the human skin. The SPF is an indicator of the protection provided for the skin against sunburn from ultraviolet radiation, and is obtained by dividing the amount of ultraviolet radiation required to cause erythema when using a sun care product by the amount of ultraviolet radiation required to cause erythema without using the sun care product. For example, assuming ultraviolet light is irradiated under the same conditions, the degree of sunburn from exposure to ultraviolet radiation when using a sun care product with an SPF of 10 is equivalent to the degree of sunburn that may be sustained by the bare skin when being exposed to ten times the amount of ultraviolet radiation.
In determining the SPF, a solar simulator is used rather than sunlight, which may vary in intensity depending on the season or the environment. Also, the method of determining the SFP involves irradiating a fixed amount of ultraviolet light on the skin having the product applied and the skin without the product applied, and checking whether erythema has occurred the next day.
By using an SPF determined using the above method, the protective effect of a sun care product against ultraviolet radiation may be objectively evaluated. However, the above determination method requires the cooperation of a large number of human volunteers with various skin types as test subjects, and is also costly and time-consuming. Also, from an ethical standpoint, an in vitro determination method that does not involve testing on human subjects may be favored for evaluating the ultraviolet protection effect of a product still in the development stage, for example. Thus, in recent years and continuing, techniques are being developed for calculating in vitro SPF predictive values having high correlation with in vivo SPF values by basically re-creating the in vivo SPF determination method (See, e.g., Japanese Patent No. 4365452, and Japanese Patent No. 4454695).
It is noted that various accommodations are made with regard to measurement conditions to reduce the burden on human test subjects in the in vivo SPF determination methods currently being used.
For example, according to one technique, to reduce the measurement time, light at an intensity several tens of times stronger than the intensity of actual sunlight is irradiated on the skin so that an erythema reaction would occur sooner. According to another technique, to facilitate visual evaluation of only an erythema reaction from ultraviolet radiation, visible light and infrared light are cut out from the irradiation spectrum of a solar simulator so that redness of the skin due to the effects of heat may be prevented from occurring. However, these measurement conditions are different from irradiation conditions of actual sunlight under which the sun care product is used in real-life.
Also, in the in vivo SPF determination method, the amount of a sample applied to the skin (application dose) is uniformly fixed at 2.00 mg/cm2. However, in real-life, there are variations in the amount and manner in which a user applies a sun care product. There are publications that suggest that on average, users apply sunscreen at approximately 0.5-1.5 mg/cm2 (See, e.g., Sunscreen isn't enough, Journal of Photochemistry and Photobiology B: Biology 64 (2001) 105-108).
Although SPF values obtained using conventional in vivo SPF determination methods enable “relative” comparison of the ultraviolet protection effects of different products, they do not provide predictions based on a quantitative “absolute” measure of the “ultraviolet protection effect under actual usage environments and usage conditions” for each individual user.
Thus, even when a consumer uses a product with an SPF value suitable for a particular scene, the user may still sustain sunburns. It has been believed that this is primarily due to discrepancies in the usage conditions of the consumer such as the application dose by the consumer being less than the application dose used in the in vivo SPF determination method or unevenness of application.
It is important from a consumer protection standpoint to provide information predicting the ultraviolet protection effect of a product under actual usage environments and usage conditions. However, an in vitro SPF evaluation method for predicting the ultraviolet protection effect based on usage environments and usage conditions in real-life (referred to as “real-life SPF” or “rSPF” hereinafter) has yet to be developed.
One reason for the absence of such in vitro SPF evaluation method may be due to the fact that SPF values obtained using the conventional in vivo SPF determination methods have been perceived as “absolute” measures of the ultraviolet protection effect.
However, with the disclosure of information on the impact of consumer usage conditions such as the actual application dose on in vivo SPF values as exemplified by the above publication, there is a growing recognition of the impact of usage conditions on the “absolute” measure of the ultraviolet protection effect.
On the other hand, the impact of the usage environment such as the shape and intensity of sunlight on the “absolute” measure of ultraviolet protection effect has not been taken under consideration.
Further, a second reason for the absence of the in vitro SPF evaluation method for predicting the real-life SPF may be due to the unavailability of a highly sensitive ultraviolet radiation detection/evaluation apparatus for evaluating the real-life SFP through in vitro testing or an evaluation program having an algorithm for accumulating the amount of ultraviolet radiation to which the skin may be exposed over time and analyzing the evaluation results based on the detected ultraviolet radiation.
Also, it is noted that evaluating the real-life SPF through in vivo testing using human test subjects is not realistically possible in consideration of the burden imposed on the human test subjects from the long hours of restraint and the difficulty of distinguishing between redness of the skin caused by infrared light contained in sunlight and erythema caused by ultraviolet radiation.
As can be appreciated from above, in vitro testing that does not cause a burden on human test subjects and does not require distinguishing erythema caused by ultraviolet radiation from redness of the skin caused by heat may be suitable for predicting the real-life SPF.
It is noted that conventional in vitro SPF evaluation methods are designed to basically re-creating an in vivo SPF method such as the world-recognized International SPF Test Method (CTFASA/COLIPA/JCIA/CTFA: May 2006). That is, these in vitro SPF evaluation methods are focused on achieving high intra-laboratory reproducibility and inter-laboratory reproducibility, and accurately predicting the in vivo SPF values that may be obtained in the event the in vivo SPF evaluation method were used. Thus, the reliability of such in vitro SPF evaluation methods is assessed based on the degree of correlation with corresponding in vivo SPF values.
In other words, these conventional in vitro SPF evaluation methods and in vivo SPF evaluation methods do not reflect the protective effect against ultraviolet radiation based on the usage environments and usage conditions of actual users. Thus, SPF values obtained from conventional evaluation methods may be inadequate as information accompanying a product from a consumer protection standpoint. For example, a user may sustain sunburns by using a sun care product under conditions or environments that are different from the conditions and environment under which the SFP value of the product was obtained from a conventional in vitro SPF evaluation method or in vivo SPF evaluation method.
Thus, a technique is desired for quantitatively predicting an “ultraviolet protection effect under actual usage environments and usage conditions” for each individual through in vitro testing.
It is an object of at least one embodiment of the present invention to provide an ultraviolet protection effect evaluation method, evaluation apparatus, and a recording medium for accurately evaluating the ultraviolet protection effect of a sample under real-life usage conditions and usage environments.